1. Field of the Invention
The present invention relates to a tube joint and a method of constructing it wherewith one end of a tubing is passed through a through-hole in a cap nut that is provided in the direction of the axis of the threaded portion of the cap nut, a drop-off prevention ring being anchored to the end of the tubing, being fitted thereto, a joint main body being fitted into the end of said tubing, the external thread of the joint main body being engaged with the internal thread of said cap nut for allowing the hole edge portion of the through-hole in said cap nut to be pressed against one end of said drop-off prevention ring, in order to provide drop-off prevention of the tubing.
2. Description of the Prior Art
Such tube joints are already known from, for example, Japanese Unexamined Patent Publication No. 8(1996)-247353, now patented as Patent No. 2756929 and Japanese Unexamined Patent Publication No. 10 (1998)-318475.
The former is a tube joint which is constructed by passing the end of a tube through the through-hole in a cap nut, upsetting the end of the tube by means of an upsetting jig, fitting a drop-off prevention ring to the end of the tube, and welding the drop-off prevention ring to the upset end of the tube by means of a heat source h disposed around the drop-off prevention ring.
Into the end of the tube to which the drop-off prevention ring is welded inserted the insertion cylinder portion of the joint main body. At this time, the drop-off prevention ring and the end of the tube are inserted into the annular groove in the joint main body. Then, by screw attaching the cap nut, with which the tube is passed through the through-hole therein, to the joint main body, a tube joint is constructed. If a force is applied to the tube in the direction of causing it to drop off, one end of the drop-off prevention ring is pressed against the hole edge portion of the cap nut, which prevents the tube from dropping off.
The latter is a tube joint which is constructed by upsetting the end of a tube, pressure fitting a shape ring into the upset end, the shape ring being formed to an angle section for providing a sloping portion for the tube, and pressing the annular anchoring protrusion of the cap nut against the sloping portion of the tube for prevention of the tube from dropping off.
However, with such conventional tube joints, there have been problems: with the former, because the end of the tube is upset, and the drop-off prevention ring is welded to the end of the tube, a device which has both an upsetting jig and a welding means including a heat source h, and thus is large-sized and complicated, is required, resulting in the cost being increased.
With the latter, a shape ring is pressure fitted into the upset end of the tube, resulting in the diameter of the end of the tube being further increased, and thus the tube is used, being subjected to a high load. Therefore, the durability is rather unsatisfactory, and the size of the cap nut to be pressed against the upset end of the tube is increased, which can be a difficulty in making the entire tube joint compact.
The present invention has been developed in consideration of these problems, and it is intended to provide a tube joint and a method of constructing it with which the drop-off prevention ring can be attached to the end of the tubing with a simple device, the cost can be reduced, the durability can be bettered, and the size of the entire tube joint can be minimized.
This purpose of the present invention can be achieved by:
[1] A tube joint wherewith one end (T1) of a tubing (T) is passed through a through-hole (22) in a cap nut (20) that is provided in the direction of the axis of the threaded portion of the cap nut (20), a drop-off prevention ring (30) being anchored to the end (T1) of the tubing (T), being fitted thereto, a joint main body (10) being fitted into the end (T1) of said tubing (T), the external thread (15) of the joint main body (10) being engaged with the internal thread (25) of said cap nut (20) for allowing the hole edge portion of the through-hole (22) in said cap nut (20) to be pressed against one end of said drop-off prevention ring (30), in order to provide drop-off prevention of the tubing (T), wherein
said drop-off prevention ring (30) has an anchoring portion (35) which projects from the bore surface thereof toward the inside; and
said anchoring portion (35) bites into the end (T1) of said tubing (T), being anchored thereto.
[2] A method of constructing a tube joint wherewith one end (T1) of a tubing (T) is passed through a through-hole (22) in a cap nut (20) that is provided in the direction of the axis of the threaded portion of the cap nut (20), a drop-off prevention ring (30) being anchored to the end (T1) of the tubing (T), being fitted thereto, a joint main body (10) being fitted into the end (T1) of said tubing (T), the external thread (15) of the joint main body (10) being engaged with the internal thread (25) of said cap nut (20) for allowing the hole edge portion of the through-hole (22) in said cap nut (20) to be pressed against one end of said drop-off prevention ring (30), in order to provide drop-off prevention of the tubing (T), comprising the steps of:
fitting the end (T1) of said tubing (T) that is softened by heating, into said drop-off prevention ring (30);
causing said anchoring portion (35) which projects from the bore surface thereof toward the inside, to bite into the softened end (T1) of said tubing (T); and
cooling the end (T1) of said tubing (T) for hardening it with said anchoring portion (35) biting into the end (T1) of said tubing (T).
[3] The tube joint according to [1] or the method of constructing a tube joint according to [2], wherein said anchoring portion (35) is projected along a plane perpendicular to the central axis of said drop-off prevention ring (30) or it is projected slantwise with respect to the perpendicular plane and toward the end of the drop-off prevention ring (30) that is opposite to the end of said drop-off prevention ring (30) which can be pressed against the hole edge portion of the through-hole (22) in said cap nut (20).
[4] The tube joint or the method of constructing a tube joint according to [3], wherein the anchoring portion (35) is formed annularly along the circumference of the bore surface of the drop-off prevention ring (30), and a plurality of anchoring portions are provided in the direction perpendicular to said circumference.
[5] The tube joint according to [1] or the method of constructing a tube joint according to [2], wherein the one end of said drop-off prevention ring (30) has a thin-wall section (33) which can be elastically deformed when pressed against the hole edge portion of the through-hole (22) in said cap nut (20).
[6] The method of constructing a tube joint according to any one of [2] to [5], wherein the end (T1) of said tubing (T) that is softened by heating is fitted into said drop-off prevention ring (30), and by upsetting the softened end (T1) of said tubing (T), the anchoring portion (35) of said drop-off prevention ring (30) is caused to bite into the end (T1) of the tubing (T).
[7] The tube joint according to any one of [1] and [3] to [5], wherein the end (T1) of said tubing (T) is upset, and said anchoring portion (35) bites into the upset end (T1) of said tubing (T), being anchored thereto.
The functions of the inventions as stated in the above paragraphs [1] to [7] will be described here.
By softening the end (T1) of a tubing (T) by some means, the anchoring portion (35) of a drop-off prevention ring (30) is allowed to easily bite into the softened end (T1) of the tubing (T).
When the end (T1) of the tubing (T) into which the anchoring portion (35) bites is cooled, it is hardened with the anchoring portion (35) of the drop-off prevention ring (30) biting into it, thus, the drop-off prevention ring (30) can be attached to the end (T1) of the tubing (T) with ease.
By using, for example, an upsetting jig, a drop-off prevention ring (30) can be simply attached to one end (T1) of a tubing (T).
In particular, the drop-off prevention ring (30) is fitted into the holding hole (47) of the support cylinder (40) in the upsetting jig. Into the holding hole (47) of the support cylinder (40) is inserted the end (T1) of the tubing (T) that is softened by, for example, heating. Then, an annular clearance is formed between the end (T1) of the tubing (T) and the drop-off prevention ring (30). The anchoring portion (35) of the drop-off prevention ring (30) is projected toward the end (T1) of the tubing (T).
Then, fitting the upsetting core (50) in the upsetting jig into the end (T1) of the tubing (T) will easily upset the end (T1) of the tubing (T) because it is softened, and at the same time, cause the anchoring portion (35) of the drop-off prevention ring (30) to bite into the softened and upset end (T1) of the tubing (T) with ease.
Then, cooling the end (T1) of the tubing (T) naturally or positively will harden it with the anchoring portion (35) of the drop-off prevention ring (30) being kept biting into the end (T1) of the tubing (T). Thus, the drop-off prevention ring (30) can be simply attached to the end (T1) of the tubing (T).
With a tube joint which comprises a drop-off prevention ring (30) attached to one end (T1) of a tubing (T), if a force is applied to the tubing (T) in the direction of causing it to drop off, one end (31) of the drop-off prevention ring (30) is pressed against the hole edge portion of the through-hole (22) in the cap nut (20), which prevents the tubing (T) from dropping off. The reaction force caused when the one end (31) of the drop-off prevention ring (30) is pressed against the hole edge portion of the through-hole (22) in the cap nut (20) provides a force in the direction from the one end (31) of the drop-off prevention ring (30) toward the other end (32), i.e., a force in the direction of removing the drop-off prevention ring (30) from the end (T1) of the tubing (T).
However, because the anchoring portion (35) of the drop-off prevention ring (30) is projected along a plane perpendicular to the central axis of the drop-off prevention ring (30) or it is projected slantwise with respect to the perpendicular plane and toward the other end (32) of the drop-off prevention ring (30) that is opposite to the one end (31) of the drop-off prevention ring (30) which can be pressed against the hole edge portion of the through-hole (22) in the cap nut (20), the anchoring portion (35) of the drop-off prevention ring (30) is caused to further bite into the end (T1) of the tubing (T), the drop-off prevention ring (30) will not be removed from the end (T1) of the tubing (T), thus being kept attached to the end (T1) of the tubing (T).
The anchoring portion (35) may be provided in various geometries and numbers. For example, when it is formed annularly along the circumference of the bore surface of the drop-off prevention ring (30), and a plurality of anchoring portions are provided along the central axis of the drop-off prevention ring (30), the anchoring portions (35) can sufficiently resist a high force which might be applied to the tubing (T) in the direction of causing it to drop off. A number of annular anchoring portions (35) may be provided over the entire bore surface of the drop-off prevention ring (30).
By periodically retightening the cap nut (20), the tube joint is maintained in the proper condition. As the cap nut (20) is retightened, the distance between the hole edge portion of the through-hole (22) in the cap nut (20) and the one end (31) of the drop-off prevention ring (30) is decreased, and finally the hole edge portion of the through-hole (22) reaches the one end (31) of the drop-off prevention ring (30) to press it. However, at the one end (31) of the drop-off prevention ring (30), a thin-wall section (33) is formed, and this thin-wall section (33) can be elastically deformed when pressed against the hole edge portion of the through-hole (22) in the cap nut (20), which allows easy retightening of the cap nut (20). In addition, the thin-wall section (33) will accommodate the reaction force to the drop-off prevention ring (30) that is caused when the thin-wall section (33) is pressed against the hole edge portion of the through-hole (22), which eliminates the possibility of the drop-off prevention ring (30) being removed from the end (T1) of the tubing (T). Further, the adverse effect on the sealing point (the point where the tubing (T) is sandwiched between the hole edge (221) of the through-hole (22) in the cap nut (20) and the end (121) of the connecting cylinder (12) of the joint main body (10)) can be minimized.